Touch panels are a particular class of electronic visual displays, which are able to detect and locate a touch within a display area. Generally, touch panels include a transparent body disposed over a screen and configured to sense a touch. Such a body is substantially transparent, so that light in the visible spectrum emitted by the screen can be transmitted therethrough. At least some known touch panels include a transparent body constituted by a barrier and a transparent conductor formed, in this order, over a substrate. A touch on the display area of such a panel generally results in a measurable change of capacitance in a region of the transparent body. The change in capacitance may be measured using different technologies, so that the position of the touch can be determined.
A transparent body for use with a touch panel is subject to some particular requirements. In particular, one key requirement is that the transparent body is stable enough for withstanding multiple contacts on the screen and harsh conditions, so that reliability of the touch screen is not compromised over time. However, at least some known transparent bodies included in touch screens, which are considered robust, interfere with a proper transmission of light therethrough due to, for example, thickness, composition, and structure of the layers forming the transparent body. Furthermore, fabricating such a stable transparent body of high quality, for example with a uniform and defect-free barrier, is challenging.
Further, it is to be considered that there are different types of transparent bodies for touch panels. Particular consideration of the optical characteristics, e.g. the appearance to a user, has to be taken into account for transparent bodies, wherein the conductive layer for measuring the change in capacitance is a structured conductive layer.
A further aspect to be considered is the steadily increasing size of displays, wherein beyond the optical characteristics described above, also the electrical characteristics are of increasing interest. Thereby, a design of thin film based flat panel displays and touch screen technologies which provides an invisible object, which is patterned with respect to conductivity (like a touch sensor structure) and which exhibits enhanced optical and electrical performance compared to conventional structures, is desired.
Generally, it is desirable to provide touch panels from an unbreakable material. Thus, plastic foils would be a suitable substrate. However, processing of foils is even more challenging, e.g. due to their limited capability to be heated. Accordingly, larger sized projective capacitive touch panel sensors based on rugged, unbreakable, PET foil substrates, require specific electrical properties, high optical and color neutral transmission in combination with the invisibility of the sensor elements after patterning.
Accordingly, it is desirable to have a process and an apparatus for forming a high-quality transparent body for use in a touch panel in a manner such that the body is stably formed over the substrate without compromising a proper transmission of light in the visible spectrum and improved electrical characteristics.